1. Field of the Invention
The present invention relates to a method of manufacturing an image display medium, and more specifically to a method of manufacturing an image display medium that can display an image repeatedly, and to an image display medium.
2. Description of the Related Art
Hitherto, electronic paper technology for displaying desired images on a display substrate utilizing an electric power has become known. When broadly classified, such electronic paper technology includes constructions in which a liquid display element or a display liquid with a display element dispersed in a liquid is encapsulated between opposed substrates, as in the case of technologies such as electrophoresis, thermal rewritability, liquid crystals, and electrochromy are used, and constructions in which a powder-type display element such as a toner is encapsulated between the opposed substrates, as in the case of a construction in which conductive coloring toner 96 and white particles 98 are encapsulated between two display substrates 90a, 90b each constructed with a matrix electrode 92 and an electric charge transferring layer 94 laminated in sequence, as shown in FIG. 20.
A method of manufacturing electronic paper in the former construction, in which a liquid display element or a display liquid obtained by dispersing a display element in a liquid is encapsulated between the opposed substrates, is generally known. For example, a liquid crystal display is produced by forming a vacuum between the substrates and causing the liquid display element, or the display liquid with the display element dispersed in the liquid, to be sucked between the substrates.
However, a method of manufacturing electronic paper in the latter construction, in which a powder-type display element such as toner is encapsulated between the opposed substrates, is not generally known. A method comprising steps of dispersing powder bodies in carrier fluid, filling the carrier fluid from an opening into a vacuumed space between substrates, and evaporating the carrier fluid is conceivable as a technique for producing electronic paper with such a construction. However, this is difficult and it is not practical to completely evaporate the carrier fluid filled between the substrates from the opening. In addition, when the substrates are fixed by a spacer, a problem of deterioration of display due to trapping of the powder bodies may arise.
Accordingly, it is an object of the present invention to encapsulate a prescribed amount of a powder-type display element uniformly between opposed substrates. It is another object of the present invention to provide a method of manufacturing an image display medium, and an image display medium, in which a powder-type display element can be encapsulated uniformly between opposed substrates and irregularities in displayed images due to trapping of powder bodies may be prevented.
In order to achieve the objects described above, a method of manufacturing an image display medium according to a first aspect of the present invention includes steps of: providing substantially flat substrates, one of which having at least one spacer disposed thereon; disposing a plurality of color material particles distributed substantially uniformly on at least one of the substrates; while maintaining a predetermined amount of the plurality of color material particles distributed on the at least one substrate, superimposing another substrate thereon; and using the at least one spacer to fix the substrates to one another.
That is, according to the first aspect of the present invention, a prescribed amount of the color material particles is encapsulated uniformly between two opposed substrates by fixing the first substrate and the spacer of the second substrate in a state in which the color material particles are held on the first substrate, the spacer-side of the second substrate, or both the first substrate and the spacer-side of the second substrate.
Especially, when using two types of color material particles having different electrostatic properties, it is preferable to attach the color material particles having one of the electrostatic properties to the first substrate and the color material particles having the other electrostatic property to the spacer-side of the second substrate.
In other words, since the first substrate and the spacer of the second substrate are fixed with each other in the method of manufacturing the image display medium according to the first aspect, the distance between the first substrate and the second substrate is kept constant. In addition, since the color material particles are held on at least one of the substrates, the color material particles can be encapsulated uniformly over the whole area thereof without causing a disadvantage that the amount of the color material particles encapsulated between the first substrate and the second substrate varies between areas divided by the spacer, including a case where some areas have no color material particles at all.
In order to distribute the color material particles uniformly, the color material particles may be attached to one or both of the first and the second substrates by transferring the particles a prescribed distance by an electric field.
For example, a method utilizing an electrostatic recording system, which includes steps of charging the color material particles and attaching the charged color material particles directly to a substrate formed with an electrostatic latent image on a surface thereof, or of attaching the charged color material particles to an intermediate transfer body formed with an electrostatic latent image on a surface thereof, and then transferring the charged color material particles from the intermediate transfer body to the substrate, may be employed. In addition, the color material particles can be applied in a desired pattern by using electrostatic recording methods such as electrophotographic technology, a multi-stylus electrode, liquid development, electrostatic application, and so on.
Alternatively, a method of simply supplying the color material particles to the substrate and holding the particles on the substrate or the like may be employed. Examples of this method include screen printing, blade coating, roll coating, spray coating, gap coating, and bar coating, and the layer of color material particles may be applied on the substrate by supplying the color material particles with these methods.
Alternatively, the color material particles may be distributed uniformly by dispersing the color material particles in gas and supplying the gas to at least one of the first and the second substrates.
For example, a particle falling method, in which the color material particles are suspended in a space by air blowing or the like, and the substrate is held or passed in the space for a predetermined period of time so that the color material particles are allowed to drop down to form a uniform layer of color material particles on the substrate, may be employed.
Alternatively, a method using magnetic recording, in which color material particles including magnetic bodies therein are held directly on a substrate formed with a magnetic pattern on the surface thereof, or the color material particles are held on an intermediate transfer body formed with a magnetic pattern on the surface thereof and then transferred from the intermediate transfer body to the substrate and held thereon, may be employed. By using magnetography as a magnetic recording method, the color material particles can be applied in a desired pattern.
The color material particles can also be distributed uniformly by supplying them to at least one of the first substrate and the second substrate in a state of being dispersed in a liquid.
For example, a method which includes steps of dispersing the color material particles in a carrier fluid, holding the carrier fluid including the color material particles on the surface of a substrate, and evaporating the carrier fluid so that only the color material particles remain held on the substrate may be employed. For example, a uniform layer of color material particles may be formed on the substrate by applying the color material particles on the substrate by screen printing, blade coating, roll coating, spray coating, gap coating, bar coating, or application by means of a liquid injection device such as an inkjet, and dehydrating to evaporate the carrier fluid.
Another method, which includes steps of supplying the color material particles directly on the substrate, and shaking the substrate so that the color material particles on the substrate are uniformly distributed and held on the substrate, may also be employed. In this method, a uniform layer of color material particles can be applied on the substrate by carrying out cascade development of the color material particles on the substrate, and then shaking the substrate to form a uniform layer of developed color material particles on the substrate. This step of shaking the substrate is also effective in the above-described screen printing, blade coating, roll coating, spray coating, gap coating, bar coating, and particle falling methods.
In addition, a method which includes steps of applying the color material particles on a substrate applied with a volatile liquid in a desired pattern, and holding the color material particles on the volatile liquid so that the color material particles are attached on the substrate in the desired pattern may also be employed. In this method, the layer of color material particles in the desired pattern can be applied on the substrate by supplying and holding the color material particles to the substrate applied with the volatile liquid in the desired pattern by a screen printing, blade coating, roll coating, spray coating, or particle falling method, blowing off excess particles held on areas other than the pattern, and evaporating the volatile liquid.
Still another method, which includes steps of placing a mask having openings arranged in a desired pattern on the substrate, supplying the particles and removing the mask, may be employed for attaching the color material particles on the substrate in a desired pattern. In this method, the color material particles may be applied on the substrate in the desired pattern by placing the mask having openings arranged in the desired pattern on the substrate, supplying the particles to the substrate by a screen printing, blade coating, roll coating, spray coating, gap coating, bar coating, or particle falling method, and removing the mask.
The spacer on the second substrate may be formed by cutting or sandblasting the surface of the flat substrate by the use of a cutting tool, a laser, or the like, or by patterning the substrate by the use of lithography.
A second substrate provided with a spacer may be formed by filling a mold having a casting surface of a spacer pattern with a spacer material and curing same, or by molding same as a second substrate by hot pressing. According to this method, the spacer can be formed in a complicated and precise pattern with a manufacturing method suitable for mass production, thereby enabling an increase in resolution of the displayed images by manufacturing a mold with a desired pattern in advance by a microfabrication technology such as electric-discharge machining, and then curing the mold by ultraviolet rays, visible light rays, or an electron beam, using a stimulation-curable resin such as a UV-curable resin, a visible light-curable resin, or an electron beam-curable cured resin, or by molding a thermoplastic resin by hot press, and curing by cooling.
The spacer on the second substrate may be formed by fixing the spacer after it has been disposed on the flat substrate.
For example, a spacer may be formed by the steps of dispersing spacer particles in adhesive carrier fluid to obtain a dispersion fluid, spraying the obtained dispersion fluid on a flat substrate by a liquid injecting apparatus such as an inkjet recording device and sticking the spacer particles on the substrate by the adhesive property of the carrier fluid, or by steps of dispersing the spacer particles into a volatile carrier fluid, supplying the fluid to a flat substrate formed with a sticky layer, evaporating the carrier fluid, and sticking the spacer particles to the substrate by sticking force of the sticky layer formed on the surface of the substrate.
The sticky layer may be any one of an adhesive layer formed of an adhesive agent, a layer of thermoplastic resin that is plasticizable by application of heat, or a layer of stimulation-curable resin. The stimulation-curable resin that can be used here includes, for example, a UV-curable resin that is cured by ultraviolet rays, a visible light curable resin that is cured by a visible light, and an electron beam-curable resin that is cured by an electron beam.
When a sticky layer of thermoplastic resin is employed, the spacer particles can be fixed on the second substrate by steps of evaporating the carrier fluid, heating to plasticize, and cooling down. According to this method, a substrate having a spacer can be fabricated in a simple and inexpensive manner.
Alternatively, if a layer of stimulation-curable resin is employed as the sticky layer formed on the substrate, the spacer particles can be fixed on the second substrate by the steps of evaporating the carrier fluid, and curing by applying stimulation such as visible light, ultraviolet rays, heat, or an electron beam.
The spacer may also be formed by supplying spacer particles formed with sticking layers on surfaces thereof or spacer particles formed of a thermoplastic resin or a stimulation-curable resin to the flat substrate and fixing them on the substrate by sticking force of the sticky layer on the surfaces of the spacer particles. This sticky layer has the same construction as described above, and thus will not be described again.
For example, a method utilizing the electrostatic recording method, including steps of charging spacer particles, and attaching the charged spacer particles directly on a substrate formed with an electrostatic latent image on the surface thereof, or steps of attaching charged spacer particles on an intermediate transfer body formed with an electrostatic latent image on the surface thereof, transferring the charged spacer particles from the intermediate transfer body to the substrate, and attaching them on the substrate, may be employed. The spacer particles may be applied in a desired pattern by using an electrostatic recording method such as electrophotographic technology, a multi-stylus electrode, liquid development, and electrostatic applications.
The sticky layer may be a layer of thermoplastic resin that is plasticizable by application of heat. The spacer particles may be fixed on the second substrate by heating and plasticizing the sticky layer, and cooling it down. According to this method, a substrate having a spacer may be fabricated in a simple and inexpensive manner.
Alternatively, other methods, including steps of providing spacer particles having magnetic bodies therein, attaching the spacer particles directly on a substrate formed with a magnetic pattern on the surface thereof; or steps of attaching the spacer particles on an intermediate transfer body formed with a magnetic pattern on the surface thereof and transferring and attaching the spacer particles from the intermediate transfer body to the substrate; or steps of disposing a magnetic body or electromagnet formed into a given pattern on a back side of a substrate, attaching the spacer particles on a front surface of the substrate, and removing the magnetic body or turning off the electromagnet, may be employed. When using magnetography as a magnetic recording method, the spacer particles maybe applied in a desired pattern, and fixed on the substrate by sticking force of the sticky layer on the surface of the spacer particles. The sticky layer has the same construction as described above, and thus will not be described again.
In addition, a method including steps of dispersing the spacer particles in a carrier fluid, attaching the carrier fluid on the surface of the substrate, and then evaporating the same so that only the spacer particles remains attached on the substrate may be employed. For example, a method of forming a spacer that includes steps of applying the spacer particles on the substrate by screen printing, blade coating, roll coating, spray coating, gap coating, bar coating, or application by means of a liquid injection device such as an inkjet, and fixing the spacer particles on the substrate by sticking force of the sticky layer on the surface of the spacer particles may be employed. The sticky layer has the same construction as described above, and thus will not be described again.
In addition, a method which includes steps of applying spacer particles on a substrate applied with a volatile liquid in a desired pattern, and attaching the spacer particles on the volatile liquid so that the spacer particles are attached on the substrate in a desired pattern may be employed. For example, a method of forming a spacer which includes steps of supplying and attaching the spacer particles on the substrate applied with a volatile liquid in a desired pattern by screen printing, blade coating, roll coating, spray coating, or the particle falling method, blowing off excess spacer particles attached in an area other than the pattern with air or the like, and evaporating the volatile liquid may be employed so that the spacer particles are applied on the substrate in the desired pattern and fixed on the substrate by sticking force of the sticky layer on the surface of the spacer particles. The sticky layer has the same construction as described above, and thus will not be described again.
A method of attaching the spacer particles on the substrate in a desired pattern by steps of placing a mask having openings formed in a desired pattern on the substrate, supplying the spacer particles thereto, and removing the mask from the substrate may also be employed. For example, a method of forming a spacer by steps of supplying the spacer particles to the substrate with the mask having openings arranged in the desired pattern placed thereon by screen printing, blade coating, roll coating, spray coating, gap coating, bar coating, or the particle falling method, and removing the mask may also be employed so that the spacer particles are applied on the substrate in the desired pattern and fixed on the substrate by sticking force of the sticky layer on the surfaces of the spacer particles. The sticky layer has the same construction as described above, and thus will not be described again.
The spacer may be formed by forming a film of thermoplastic resin by thermal transfer application, for example, with a thermal head or the like, or by stimulating a film formed of a stimulation-curable resin. According to this method, a desired pattern may be produced by processing the substrate by hot pressing or the like, and thus the spacer may be fabricated by an inexpensive method suitable for mass production. It is also possible to use a resin obtained by mixing the spacer particles with a thermoplastic resin in advance.
The spacer to be arranged on the flat substrate may also be formed by arranging rod shaped members each provided with a surface layer of thermoplastic resin or rod shaped members each formed of a thermoplastic resin on the flat substrate, and curing them by application of heat, or by arranging rod shaped members each provided with a layer of a stimulation-curable resin or rod shaped members formed of a stimulation-curable resin on the flat substrate, and curing them by stimulation. It is also applicable to cross pluralities of rod shaped members. The thermoplastic resin and the stimulation-curable resin are the same as those described above, and thus will not be described again.
The second substrate may be applied with a film with a rough surface, obtained by mixing the spacer particles with a polymeric resin film. According to this method, by encapsulating the particles in recesses of the film and applying a thermoplastic resin and a stimulation-curable resin on projections, the second substrate can be adhered to the first substrate.
The spacer may be of any type as long as a space between the first substrate and the second substrate is kept constant. However, it is preferable to form the spacer in a grid pattern or in a mesh pattern. A number of cells are defined between the first substrate and the second substrate by forming the spacer in a grid pattern or in a mesh pattern, which prevents the color material particles from gathering to one portion of the display medium when the display medium is moved. It is also preferable because various colors can be displayed by changing the colors of the color material particles to be encapsulated in each of the divided cells.
A member with a grid pattern or a mesh pattern may be formed by forming holes in a sheet formed of metal, such as stainless steel or a resin film such as polyimide, by an etching or laser process, by depositing a metal such as nickel by electroforming, or by knitting metal wire such as stainless steel or a resin such as nylon into a mesh pattern. These members may also be coated as needed with a resin insulating material, or with a thermoplastic resin for providing an adhesive property.
The color material particles may be distributed uniformly by supplying a prescribed certain amount of color material particles from a container containing the color material particles to at least one of the first substrate and the second substrate.
It is also possible to distribute the color material particles uniformly by removing excess color material particles after supplying the color material particles to at least one of the first substrate and the second substrate.
In addition, in a second aspect of the present invention, preferably, a method of manufacturing an image display medium includes steps of: providing substantially flat substrates, one of which having at least one spacer disposed thereon, the substrates being fixable to one another using the at least one spacer interposed between the substrates; disposing a plurality of color material particles on at least one of the substrates; while maintaining the color material particles on the at least one of the substrates, superimposing the substrates such that substantially no color material particles are disposed on a surface of the at least one spacer opposing one of the substrates; and fixing the substrates to one another using the at least one spacer.
According to this aspect, the first substrate and the spacer of the second substrate are fixed in such a manner that the color material particles are held between the first substrate and the second substrate without attaching the color material particles on the surface of the spacer opposing to the first substrate. The term xe2x80x9cwithout attachingxe2x80x9d includes a case where the particles are removed after being attached.
That is, the color material particles are held on the second substrate, the color material particles being held over a whole area of an upper surface of the spacer provided on the second substrate. The first substrate is to be fixed on the upper surface of the spacer, so the color material particles attached on the upper surface of the spacer are at risk of being fixed with fixation between the spacer and the first substrate.
If the color material particles are fixed between the spacer and the first substrate, this may cause not only deterioration of an adhesive property between the spacer and the first substrate, but also deterioration of image quality, because the fixed color material particles are always visible when the side of the first substrate is used as a display surface. Therefore, although images of better quality may be obtained by using the second substrate as a display surface, removing the color material particles fixed on the upper surface of the spacer or preventing them from attaching thereon helps to improve the adhesive property between the spacer and the first substrate and to provide a display medium that always displays clear images without deterioration of image quality in either of cases where the first substrate side is used as a display surface and where the second substrate side is used as a display surface.
As measures to remove color material particles attached on the upper surface of the spacer or to prevent them from attaching thereon, for example, setting the adhesive property of the upper surface lower than that of the second substrate, and shaking the spacer to remove the color material particles on the upper surface are conceivable. In the case of removing the color material particles, moving a blade that is in contact only with the upper surface of the spacer relative to the second substrate to remove the color material particles attached on the upper surface of the spacer is possible.
Since amounts of the color material particles on the upper surface of each spacer will be almost equal with each other, when the blade and the second substrate are moved one way with respect to each other, each area divided by the spacer receives an equal amount of the color material particles, which is the amount scraped off the upper surface of one spacer. Therefore, equal amounts of color material particles are consistently held in the respective areas.
By evening out the color material particles with a blade, cell structures between the spacers or recesses may be positively filled with the color material particles in a uniform manner. More specifically, the color material particles may be filled uniformly in recesses formed on the second substrate by a member with a mesh pattern, by adhering the member with a mesh pattern on the second substrate as a spacer, applying the color material particles therein, and evening out the filled color material particles with the blade. Alternatively, amounts of the color material particles may be finely controlled by controlling tendency of the blade to follow the recesses and projections of the mesh portion, by varying elasticity of the blade member, or by controlling an angle of the blade with respect to the mesh portion, or force of pressing the mesh portion. In addition, excess color material particles on projections of the mesh member may be removed.
Alternatively, in a third aspect of the present invention, a method includes steps of: providing substantially flat substrates that are fixable to one another using at least one spacer; fixing the substrates to one another via the at least one spacer, such that there is a gap between the substrates; dispersing color material particles in a gas; supplying the color material particles dispersed in the gas to the gap; and trapping the color material particles in the gap.
In a fourth aspect of the present invention, a method includes steps of: providing substantially flat substrates that are fixable to one another using at least one spacer; fixing the substrates to one another via the at least one spacer, such that there is a gap between the substrates; dispersing color material particles in a liquid; supplying the color material particles dispersed in the liquid to the gap; and trapping the color material particles in the gap.
As has been described thus far, by supplying the color material particles in a state in which the first substrate and the second substrate are fixed via the spacer in advance, irregularities in displayed images caused by trapping of the color material particles between the substrates may be prevented.
The fifth aspect of the present invention is an image display medium including: a first substantially flat substrate; a second substantially flat substrate which includes at least one spacer, the second flat substrate being superimposed with the first flat substrate with the at least one spacer therebetween such that a substantially constant distance is maintained between the substrates; and a plurality of color material particles disposed between the substrates, wherein the spacer comprises a shape that tapers toward a side thereof facing the first flat substrate. Accordingly, the area of a contact surface between the spacer and the first substrate may be reduced, thereby preventing trapping of the color material particles between the substrates.
It is also possible to hold the plurality of color material particles on one or both of the flat first substrate and the flat second substrate, then attach the spacer member to one of the first substrate and the second substrate, and then fix the spacer member and the first substrate and the second substrate so that the color material particles and the spacer member are disposed between the first substrate and the flat second substrate.
In other words, by attaching the plurality of color material particles and the spacer member on the first substrate and then fixing the first substrate and the second substrate; or by attaching the plurality of color material particles on the first substrate, attaching the spacer member on the second substrate, and then fixing the first substrate and the second substrate; or by attaching at least one type of color material particles and the spacer member on the first substrate, attaching remaining color material particles on the second substrate, and fixing the first substrate and the second substrate; or by attaching at least one type of the color material particles on the first substrate, attaching remaining color material particles and the spacer member on the second substrate, and fixing the first substrate and the second substrate, the color material particles can be encapsulated uniformly between the opposed substrates and the process can be simplified because it is not necessary to provide a spacer on the substrate in a separate process, which is preferable.
In addition, preferably, the process is further simplified by transferring the plurality of color material particles and the spacer member to an intermediate transfer body, and then holding them from the intermediate transfer body to the flat first substrate.
The following methods, of the methods described above in relation to the first aspect, may be employed for holding the color material particles and the spacer members on the substrate.
That is, methods utilizing an electrostatic recording method, such as a method in which charged color material particles and a particulated spacer member (hereinafter referred to as spacer particles) are directly held on a substrate formed with an electrostatic latent image on a surface thereof, or a method in which the charged color material particles and the spacer particles are held on an intermediate transfer body formed with an electrostatic latent image on the surface thereof, and then the charged color material particles and the spacer particles are transferred from the intermediate transfer body to the substrate, may be employed. The color material particles and the spacer particles to be used in this method may be the same as those described in relation to the first aspect, so the descriptions will not be given again.
As other methods, methods utilizing magnetic recording, such as a method in which at least one type of color material particles having a magnetic body therein and the spacer particles are used, and the color material particles and the spacer particles are directly held on the substrate formed with a magnetic pattern on the surface thereof, or a method in which at least one type of color material particles and the spacer particles are held on an intermediate transfer body formed with a magnetic pattern on the surface thereof, and the color material particles are transferred from the intermediate transfer body and attached to the substrate, may be employed. Again, the color material particles and the spacer particles in this method may be the same as those described for the first aspect, so the descriptions will not be repeated.
It is also possible to hold the plurality of color material particles on one or both of the flat first substrate and the flat second substrate with one of the flat first substrate and the flat second substrate masked, release the mask, and then hold the spacer member on one of the first substrate and the second substrate so that the spacer member and the first substrate and the second substrate are fixed in such a manner that the color material particles and the spacer member are disposed between the first substrate and the flat second substrate.
In other words, the plurality of color material particles are attached on one or both of the flat first substrate and the flat second substrate in a state in which one of the flat first substrate and the flat second substrate is masked by a member such as a mesh. After the color material particles have been held, the mask is released, and the spacer member is held on one of the first substrate and the second substrate. Subsequently, the spacer member and the first substrate and the second substrate are fixed in such a manner that the color material particles and the spacer member are disposed between the first substrate and the flat second substrate.
In this manner the color material particles may be held on only a required portion by attaching the color material particles in the masked state. Methods described for the first aspect may be used as a method of attaching the color material particles.
The spacer member may be a member with a mesh pattern, whereby the cell construction can be produced in a simple manner.
A resilient material may be used for the spacer member or for an adhesive agent for adhering the spacer member, whereby the first substrate and the second substrate are prevented from being separated even when a vertical or lateral stress is exerted on these substrates, since the spacer member or the adhesive agent for adhering the spacer member is elastic.
The spacer member may be formed of a resin. For example, one formed by applying a resin over all the surface of the first substrate or of the second substrate, then curing the resin by the application of heat, and then pressing by a die, of a predetermined configuration having projections and recesses, may be used as a spacer.
Alternatively, a plurality of color material particles are held on one or both of a flat first substrate and a flat second substrate, which are fittable with each other, and then the first substrate and the flat second substrate are fixed by fitting with each other.
That is, the first substrate and the second substrate each has a configuration that includes prescribed projections and recesses, and thus the color material particles may be supplied into the recesses on the first substrate or the second substrate. In addition, the first substrate and the second substrate have configurations that can be fitted with each other. Thus, the projections may be utilized as spacer members, and the first substrate and the second substrate can be fixed with each other without adhering. In this way, an image display medium can be manufactured in simple steps.
Uniform application in the cells may be realized by applying an alternating current by upper and lower electrodes to make the color material particles flow, after application of the color material particles in a manner described above.
The term xe2x80x9cuniformxe2x80x9d above means a uniformity such that variations between cells are not significant and no bias is found on the surface, in other words, that no irregularity in display density can be visually recognized when images are actually displayed.
For example, in the case of an image display medium that is divided into cells (the space between the substrates is divided into sub-spaces by a spacer or the like), when the amounts of particles encapsulated in each cell differ from each other, this will be recognized as irregularities in density.
Therefore, if the area of each cell viewed from the display surface is generally equal to that of other cells, a state in which an equal amount of the particles is encapsulated in each cell is called a uniformly encapsulated state, or a uniformly supplied state.
If the area of the cell viewed from the display surface differs from cell to cell, a state in which the encapsulated amounts per unit area of the cells (volume of the particles/area of the cell, or weight of the particles/area of the cell) are almost equal with each other is called uniform.
If the image display medium is not clearly divided into cells when viewed from the display surface, the case where the encapsulated amount per unit area is equal for all of the display surface of the image display medium is called uniform. In this case, a portion of the spacers (ribs) is not included as the display surface.
The uniformity of the amounts of the particles may be inspected for example from the amount supplied per unit area, obtained by transferring the particles held on the substrate from the substrate to an adhesive tape or the like and measuring the weight (or volume) thereof.
Though irregularities in density that an observer can visually recognize differ depending on qualities of the material, color, diameter of the particles used for display, configuration of the cells, the area of the image display medium, the absolute amount of the particles encapsulated, type and brightness of a light source of illumination, irregularities in density will not be obvious and the distribution is recognized to be substantially uniform when the amounts supplied per unit area are in a range of xc2x110%. It will look quite uniform and irregularities in display density can hardly be recognized when variations are within a range of xc2x130%.